OBJECTIVE: To understand, on the molecular level, the processes involved in the initiation and regulation of nerve impulses. Experiments in progress and planned are designed to elucidate the molecular basis of bio-electrical phenomena in excitable cells. Involved in our studies are the enzyme, acetylcholinesterase, the associated acetylcholine receptor, and the ion fluxes across excitable membranes, which are initiated and controlled by the interaction of specific ligands and the receptor. Single cells and membrane preparations from the electric organ of Electrophorus electricus are used. The regulatory process observed in this relatively defined system is considered to be identical to that at a nerve synapse. It is hoped to obtain information about the mechanism of interaction of ligands with the receptor using equilibrium and kinetic measurements, about the topography of the ligand-binding sites of the receptor using specific fluorescence labels, about molecular changes in the receptor which correlate with ion flux, and about the detailed balance of ions on both sides of the membrane in presence and absence of chemical mediators. Previously, quantitative investigations of the physiological effect of interactions between chemical mediators and the receptor have been restricted to measurements on single electroplax cells. Techniques are being developed to allow quantitative studies with membrane vesicles. A variety of techniques, including flow and relaxation methods, microspectrofluorimetry, and neutron activation analysis, are being used.